For a free body diagram situation how am i supposed to know when to use fk vs fs vs ff

Orque can be calculated by multiplying the force (n) applied at 90? to the lever arm at a distance (m) from the pivot point (point of rotation), the compound si unit for the torque is n? m. if the force (at 90? to the lever arm) applied is 15 n and it is applied at 2.0 m from the pivot point (point of rotation), what is the torque on the lever?

Debbie places two shopping carts in a cart corral she pushes the first cart which then pushes a second cart what force is being exerted

How is zig zagging a form of acceleration?